EFFECT OF DAILY VOLUNTARY RUNNING ON IN-VIVO INSULIN ACTION IN RAT SKELETAL-MUSCLE AND ADIPOSE-TISSUE AS DETERMINED BY THE MICRODIALYSIS TECHNIQUE

The effect of physical training on in vivo insulin-stimulated glucose utilization in relation to glycolysis (lactate formation) in rat perip heral tissues was investigated in 8 sedentary controls (SC) and 7 volu ntary running rats (VR). We used a sequential euglycemic clamp procedu re (insulin infusion rate; 6.0, 30.0 mU/kg . min) in combination with a microdialysis technique in M. quadriceps femoris, vastus lateralis, and inguinal adipose tissue. In the clamp study, glucose infusion rate (GIR) averaged over 45-75 min during the 6.0-mU/kg . min insulin infu sion was significantly (p < 0.01) higher in VR (15.36 +/- 0.83 mg/kg . min, mean+/-SE) than in SC (10.41 +/- 0.88 mg/kg . min), and the lack of a significant difference in GIR between VR and SC was found during the 30.0-mU/kg . min insulin infusion, In these tissues, there was no significant difference in dialysate lactate levels between VR and SC in the basal state without insulin or glucose infusion, or at an insul in infusion rate of 30.0 mU/kg . min. However, dialysate lactate conce ntrations in muscle averaged over 45-75 min during the 6.0-mU/kg . min insulin clamp procedure in VR (8.51 +/- 0.71 mg/dl) were significantl y (p < 0.05) higher than in SC (6.18 +/- 0.48 mg/dl). These results in dicated that insulin action in skeletal muscle and adipose tissue coul d be evaluated in vivo by using the microdialysis technique, and that an increase in GIR in VR was, in part, explained by an increase in lac tate formation in skeletal muscle.